The term nanoceramics is well known in the ceramic field for at least two decades. Even though there are many reports that nanoceramics are superior in terms of mechanical and other properties, no comprehensive and conclusive study on the grain size dependent variation in mechanical properties. So this study was an attempt to study the property variation with grain size and yttria content for a well known ceramic, yttria stabilised zirconia. High solids content but low viscosity YSZ nanosuspensions have been slip cast into -52% dense, very homogeneous green bodies in sizes up to 60 mm in diameter. Sintering cycles have been optimised using both hybrid and conventional two-step heating to yield densities >99.5% of theoretical whilst retaining a mean grain size of <100 nm. The sintered samples have been characterised for hardness, toughness, strength, wear resistance and hydrothermal ageing resistance. The results have been compared with that of a submicron zirconia ceramic prepared using a commercial powder. The strength of the nanoceramics has been found to be very similar to that of conventional submicron ceramics, viz. -10Pa, although the fracture mechanism was different. Two toughness measurement approaches have been used, indentation and surface crack in flexure. The results indicate that the nano 1.5YSZ ceramics may be best viewed as crack, or damage, initiation resistant rather than crack propagation resistant; indentation toughness measurements as high as 14.5 MPa m 112 were observed. Micro-Raman mapping was demonstrated to be a very effective technique to map the phase transformations in zirconia. The wear mechanism of nanozirconia has been observed to be different compared to that in conventional, submicron YSZ and the wear rates to be lower, particularly under wet conditions. In addition, and potentially most usefully, the nan03YSZ ceramics appear to be completely immune to hydrothermal ageing for up to 2 weeks at 245°C & 7 bar; conditions that see a conventional, commercial submicron ceramic disintegrate completely within 1 hour.

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The topic of the Ph.D. thesis was focused on the process of sintering alumina and zirconia ceramic materials with the aim to compare kinetics of sintering sub-micro and nanoparticle systems. Zirconia ceramic powders stabilized by different amount of yttria addition in the concentration range of 0 – 8 mol% were used. The different crystal structure (secured by yttria stabilization) of zirconia, as found, did not play statistically proven role in the process of zirconia sintering. The possible influence was covered by other major factors as particle size and green body structure, which does affect sintering in general. According to the Herrings law, the formula predicting sintering temperature of materials with different particle size was defined. The predicted sintering temperatures were in good correlation with the experimental data for zirconia ceramic materials prepared from both, coarser submicrometer, and also nanometer powders. In case of alumina ceramics the predicted and experimentally observed sintering temperature values did not match very well. Mainly the nanoparticle alumina materials real sintering temperature values were markedly higher than predicted. The reason was, as shown in the work, strong agglomeration of the powders and strong irregularities of particle shape. The major role of green body microstructure in the sintering process was confirmed. The final density of ceramic materials was growing in spite of sintering temperature, which was decreasing together with pore - particle size ratio (materials with similar particle size were compared). Sintering temperature was increasing together with growing size of pores trapped in the green body structure. Clear message received from the above mentioned results was the importance of elimination of stable pores with high coordination number out off the green body microstructure during shaping ceramic green parts. Same sintering kinetics model was successfully applied on the sintering process of submicro- and also nanometer zirconia ceramics. Activation energy of nanometer zirconia was notably lower in comparison to submicrometer material. For the sintering of nanoparticle zirconia was typical so called “zero stage” of sintering, clearly visible on kinetic curves. It was found out, that processes running in zirconia “green” material during zero stage of sintering are heat activated and their activation energy was determined. Pores of submicrometer zirconia were growing in an open porosity stage of sintering just a slightly (1.3 times) compared to the nanoparticle zirconia, where the growth was much higher (5.5 times of the initial pore diameter). This difference was most probably caused by preferential sintering of agglomerates within the green bodies and by particle rearrangement processes which appears in the zero stage of sintering of nanoparticular ceramics. The technology of preparation of bulk dense ytria stabilized zirconia nanomaterial with high relative density of 99.6 % t.d. and average grain size 65nm was developed within the thesis research.

Объектом исследования являются 3 образца нанокерамики на основе Al2O3, и 4 образца кварцевых стекол: КИ, КВ, КУ, КС-4В. Цель данной работы – исследование акустических свойств, обусловленных особенностями микро- (нано)структуры двух категорий материалов микро- и оптоэлектроники – нанокерамики на основе Al2O3 и оптических кварцевых стекол. В процессе работы были: исследованы акустические свойства материалов микро- (нанокерамика на основе Al2O3) и оптоэлектроники (кварцевые стекла), исследованы оптические параметры кварцевых стекол и установлена корреляция между акустическими и оптическими параметрами. В результате исследования был создан оригинальный измерительный стенд и разработана методика измерения значений скоростей поперечных ультразвуковых волн, определены упругие характеристики нанокерамики на основе Al2O3 и кварцевых стекол, а также оптические параметры стекол. В данной работе удалось установить корреляцию между акустическими и оптическими параметрами. Используя измерения скоростей ультразвука и оптического поглощения, были определены фундаментальные характеристики образцов. Это способствует пониманию структурно-чувствительных свойств, а значит, в дальнейшем и влиять на них, создавая материалы с нужными параметрами для лучшей работы приборов микро- и оптоэлектроники. / Objects of research are 3 samples of nanoceramiсs based on Al2O3 and 4 samples of quartz glasses: KI, KU, KV, KS-4V. The aim of this work is the study of the acoustic properties due to the peculiarities of micro- (nano)structures of the two categories of micro- and optoelectronics materials: nanoceramics based on Al2O3 and optical quartz glass. The acoustic properties of materials micro- (nanoceramics based on Al2O3) and optoelectronics (quartz glass) were studied, the optical parameters of quartz glass were investigated, and a correlation between acoustic and optical parameters was found. The original test stand and the method of measuring the transverse ultrasonic waves velocities were created, the elastic characteristics of nanoceramics based on Al2O3 and optical quartz glass and the optical parameters of glass were determine. In this paper we determined a correlation between acoustic and optical parameters. Using measurements of the velocity of ultrasound and optical absorption fundamental characteristics of the samples were determined. This contributes to an understanding of structure-sensitive properties that will help create materials with the necessary parameters for the best performance of micro- and optoelectronics.